Description And Operation
DESCRIPTION
Standard with the 2.9L engine, is the Torque Vectoring type Rear Drive Unit (RDU) manufactured by ZF.
OPERATION
- The operational principle of the RDU system is based on the ability to divide the total torque available on one wheel or the another.
- In order to achieve this result, the RDU uses two sprockets installed (per side): one on the drive shaft and the other on the differential casing.
- These two sprockets are the sun gears of the gear set. Meshing with the teeth of both sun gears, are the planet gears.
- They are inserted in the satellite carrier. The satellite carriers on one side have a joint that serves to engage with the clutch discs.
- The discs of two clutch packs, one for each satellite carrier, engage partly with the joint of the satellite carrier and partly with the support of the clutch fixed to the casing outside the differential.
- For each clutch unit there is an electric Axle Actuator motor.
- The purpose of the axle actuator is to activate the clutches to slow down the satellite carrier to create a resisting torque.
- The flow of torque during a left turn is split in equal measure by the open differential of the RDU.
- Activation of the right hand axle actuator
- Flow of torque through the differential
- Flow of torque through the satellite carrier and planet gears
- The differential can improve the input/output of a curve by turning on the axle actuator to the direction of the curve.
- The above example illustrates the operation of torque vectoring during a curve (left) and with the presence of the motor torque at input to the differential.
- The Torque Vectoring Module (TVM), in order to improve entry into a curve, activates the right hand axle actuator in order to create a resisting torque to slow the satellite carrier by means of the clutch discs.
- The slowing of the satellite carrier, draws torque from the differential casing which, through the planet gears, arrives at the drive shaft thus acting to unbalance the torque that arrives at the wheels.
- Activation of the right hand axle actuator
- Flow of torque through the differential
- Flow of torque through the satellite carrier and planet gears
- The above example illustrates the operation of the torque vectoring during a curve (left) and with the absence of the torque at input to the differential.
- The TVM module activates the axle actuator external to the direction of the curve to create a resistant torque.
- The torque that arrives at the differential casing is generated by the movement of the wheels in contact with the ground surface and not from the axle actuator; consequently the torque that arrives at the differential casing is partly absorbed by the slowdown of the satellite carrier and by means of planet gear input to the drive shaft.
- The result is that on the two wheels there is an unbalance of torque that acts to improve the input/output of the curve.
- Speed satellite carrier
- Wheel RPM
- Straight run
- Driving on curve (left)
- The above example shows the trend of the wheels' RPM and of the satellite carrier while travelling in a straight line or in a curve (left) in the RDU.
- When driving straight ahead, the epicyclic gear set rotates as a single assembly.
- Upon entering a curve, without torque delivered by the motor, a negative torque of equal intensity is applied to both drive wheels to stabilize deceleration.
- As the driver turns the steering wheel to arrive at the apex, a negative torque is smoothly transferred to the internal drive wheel to help the car turn.
- During the rotation of the steering wheel, next to the apex, as soon as the engine restores torque, more torque is transferred to the outside driving wheel of the curve to increase stability.
- With the increase in power, more torque is transferred to the external driving wheel to speed up the exit of the car from the curve.